As gasoline supplies become more scarce and costly, the need for fuel conservation becomes more readily apparent. Accordingly, alternate sources of fuels and methods of fuel conservation have become more attractive, particularly for internal combustion engines for automotive use.
It is known that operation of an internal combustion engine simultaneously on a liquid fuel and a gaseous fuel will increase fuel economy and engine efficiency while at the same time maintaining low levels of undesirable exhaust emissions. Vehicles adapted to run simultaneously on a liquid fuel and a gaseous fuel are sometimes called "dual fuel" or "multi-fuel" vehicles.
The theory by which gaseous fuel injection results in increased liquid fuel economy and decreased emissions is due to the presence of the gaseous fuel surrounding the liquid fuel molecules allowing increased heat to volatilize the liquid fuel in the cylinder, allowing the liquid fuel molecules to form into gaseous fuel to gain energy at the start of combustion causing a maximum release of energy from the liquid fuel. Without the insertion of the gaseous fuel the liquid fuel does not completely volatilize.
With the insertion of the gaseous fuel, once the air-fuel mixture is ignited by electrical discharge of the spark plug, instantaneous oxidation of the fuel mixture occurs and it bursts into flames. The high-energy collisions caused by this rapid volatilization and oxidation dissociate molecules into atoms, or free radicals at greater speed. These molecular fragments therefore react with greater ease and combustion takes place immediately. The wave of combustion is thereby intensified throughout the explosive mixture and occurs at the start of the cycle.
With the addition of gaseous fuel, substantially instantaneous combustion occurs at the start of the piston movement in a substantially constant volume process. In comparison, without the gaseous fuel insertion, the combustion of the liquid fuel occurs throughout the travel of the piston and unburned fuel is still present at the end of the combustion cycle.
Due to this constant volume combustion resulting from the presence of the gaseous fuel molecules, the fuel mixture is totally consumed, resulting in reduced pollutants and unburned fuel hydrocarbons being ported out of the exhaust manifold. This increased combustion also results in less heat being produced in the engine since the energy is being consumed instead of wasted as heat output. In addition, this spontaneous combustion causes higher in-cylinder gas velocity that reduces knock resistance and allows the engine to operate knock free on lower octane rated liquid fuels.
For purposes of the present application, liquid fuel is fuel which is in the liquid phase at ambient atmospheric pressure and temperature. The liquid fuels used by dual or multi fuel vehicles include any combustible liquid fuel that can be utilizable by an internal combustion engine, such as gasoline, diesel, renewable fuels such as alcohol, ethanol, methanol, etc.
The term gaseous fuels as used herein means combustible fuels which are gaseous at standard temperature and pressure. The gaseous fuels used by dual fuel vehicles include methane/natural gas (CNG), hydrogen, sewer gas, etc.
The term gaseous fuels also includes liquified petroleum gas (LPG). LPG is particularly desirable as gaseous fuel. LPG under pressure may be either in the gaseous phase, the liquid phase, or both. Common examples of LPG are propane and butane.
A dual or multi fuel internal combustion vehicle is described in U.S. Pat. No. 4,373,493. For purposes of the present invention, a "dual" or "multi" fuel vehicle or engine is one intended to run on both liquid and gaseous fuels at the same time.
In the system described in U.S. Pat. No. 4,373,493, the gaseous and liquid fuels are fed from separate fuel supplies to be burned in a standard internal combustion engine. The liquid fuel is delivered to a standard carburetor for delivering and mixing of the liquid fuel with the intake air. The idling adjustment screw of the carburetor for the gasoline is adjusted to reduce the flow of the gasoline at the idle condition.
Although the system described in U.S. Pat. No. 4,373,493 functions satisfactorily on carburetor vehicles, recent internal combustion engines have had their fuel and emission control systems updated to include the use of computers, sensors and injectors to control the liquid fuel delivery. It is a discovery of the present invention that such computers and sensors intended for use on an existing liquid fuel only vehicles may be employed without alteration in a dual fuel vehicle. Therefore, in the present invention, the idling adjustment is replaced by the computer and sensors and the constant flow of gaseous fuel allows the liquid fuel to be turned off by the updated control system.
The system disclosed in U.S. Pat. No. 4,373,493 discloses three different types of gaseous fuel reservoirs, one of which is a vertical cylindrical vessel located near the trunk, another of which is a generally flat reservoir constructed as an extension of the existing gasoline tank, and another of which is a single reservoir having a generally rectangular configuration mounted generally horizontally on the underside of the car, between the front and rear axles.
Furthermore, if LPG is stored in these reservoirs, it is difficult to fill to the appropriate level (approximately 80% full) without use of a "spit valve". A spit valve results in discharge of LPG to the environment during the filling operations. Sloshing of LPG in the reservoir or fuel lines due to motion of the vehicle can also cause slugs of liquid LPG to periodically enter the gaseous fuel line leading to the engine intake manifold, resulting at times in uneven and uncontrolled flow of gaseous fuel to the engine.
U.S. Pat. No. 4,373,493 discloses locating the LPG fuel fill at the rear of the vehicle. Although this is satisfactory for many purposes, the rear of the vehicle is subject to being struck from behind in an accident, raising the potential of damage to the gaseous fill line.
Since the rate at which gaseous fuel is used in the system described in U.S. Pat. No. 4,373,493 may vary depending upon engine volume displacement, the amount of gaseous fuel remaining at any given time can be estimated only with some difficulty. Furthermore, where LPG is used as the gaseous fuel, the potential for sloshing of the liquid LPG in the horizontal storage reservoir during motion of the vehicle makes it difficult to determine the amount of LPG remaining at any given time by means of a conventional fuel gauge.